Wireless power transmission system for free-position wireless charging of multiple devices

ABSTRACT

The present invention relates to a near-field wireless power transfer system capable of having a constant efficiency regardless of a charging position of a receiver by only using a simple impedance matching circuit without using a separate existing complex adaptive impedance matching circuit or control circuit, and simultaneously transmitting power without having difficulty with impedance matching even for wireless power transmission to a plurality of electronic devices by applying a structure having a uniform mutual inductance between a wireless power transmitter and receiver.

TECHNICAL FIELD

The present invention relates generally to a near-field wireless powertransfer system and, more particularly, to a near-field wireless powertransfer system using a structure in which wireless power transmitterand receiver have uniform mutual inductance therebetween.

BACKGROUND ART

FIG. 1 illustrates an equivalent circuit of a typical electromagneticinduction-type wireless power transfer system using respective resonantcoils of a transmitter and a receiver. When the self-inductance,resistance, and capacitance for resonance of a transmitting coil (Txcoil) are L₁, R₁, and C₁, respectively, and the self-inductance,resistance, and capacitance for resonance of a receiving coil (Rx coil)are L₂, R₂, and C₂, respectively, the power of the Tx coil that receivesan Alternating Current (AC) source Vs may be transferred to a load(impedance Z_(L)) connected to the Rx coil depending on magneticcoupling based on mutual inductance M₁₂. The load may include arectifying circuit, DC-DC converter, a controlling circuit, a batterycharger, etc. A power transmission unit including the Tx coil isprovided in a transmitter for power transmission, and a power receptionunit including the Rx coil is provided in various types of electronicdevices that consume power, such as a smart phone and an iPad. Anelectronic device may be located close to the power transmission unitand allow power to be supplied to the load of the electronic device in awireless manner through the Rx coil of the electronic device.

However, in the wireless power transfer system, the intensity ofmagnetic coupling between the above-described Tx and Rx coils varieswith the structures, geometrical arrangement, and positions of the Txand Rx coils and a distance between the Tx and Rx coils. When theintensity of magnetic coupling between the transmitting and receivingcoils varies depending on various environmental changes, the optimalpower transfer condition of a wireless power transfer system changes.Thus, complexity is required in such a way that an additional impedancematching circuit is provided in the transmitter or receiver to satisfythe condition of the maximum power transfer, or a current voltagesensing circuit or the like is provided so as to control the optimalpower transfer condition. In particular, when a plate-type transmitteris used, optimal impedance matching between the transmitter and thereceiver must be realized depending on the position of the receiverplaced on a plate, and thus a problem arises in that it is difficult tosupport wireless power transmission at a free position (freepositioning) between the transmitter and the receiver. Further, whenmutual inductance between the transmitting and receiving coils differsfor each position, or when multiple devices are located at differentpositions to receive power, a problem arises in that it is difficult forthe transmitter to perform impedance matching to respective devices fordifferent impedances, thus making it impossible to simultaneouslysupport power transmission to multiple devices.

In relation to conventional wireless power transmission technology formaximum power transfer between a transmitter and a receiver, variousdocuments are published, and the following four documents among thedocuments are introduced below.

-   (1) A. Kurs, A. Karalis, R. Moffatt, J. D. Joannopoulos, P. Fisher,    and M. Soljacic, “Wireless power transfer via strongly coupled    magnetic resonances”, Science, vol. 317, pp. 83-86, July 2007.-   (2) J. Park, Y. Tak, Y. Kim, Y. Kim, S. Nam, “Investigation of    adaptive matching methods for near-field wireless power transfer”,    IEEE Transactions on Antennas and Propagation, vol. 59, pp.    1769-1773, May 2011.-   (3) W. S. Lee, H. L. Lee, K. S. Oh, and J. W. Yu, “Uniform magnetic    field distribution of a spatially structured resonant coil for    wireless power transfer”, Applied physics Letters 100, 2012.-   (4) W. S. Lee, W. I. Son, K. S. Oh, and J. W. Yu, “Contactless    energy transfer systems using antiparallel resonant loops”, IEEE    transactions on industrial electronics, Vol. 60, No. 1, January    2013.

In the above document (1), a maximum power transfer condition thatvaries with a change in distance has been satisfied by additionallyusing transmission/reception coupling coils in addition totransmission/reception resonant coils. However, this method isproblematic in that it is difficult to apply such a method to a limitedspace when the limited space is used because the addedtransmitting/receiving coupling coils must be physically moved.

The above document (2) discloses a configuration that uses the splittingof transmission/reception penetration characteristics appearing whilecoupling changes according to the distance, as a method of tracking anoptimal frequency so as to transfer the maximum power according to thedistance between the transmitting/receiving resonant coils. However,there is a problem in that, when the frequency for near-field wirelesspower transfer is fixed, it is difficult to use such a frequencytracking method.

The above document (3) proposes a structure of having a uniform magneticfield distribution at a predetermined height of a rectangular coil bybending the rectangular coil, but it is disadvantageous in that theshape of the coil must be mechanically deformed. Also, there is adisadvantage in that, unless the receiver has a uniform magnetic field,uniform mutual inductance or a uniform figure of merit cannot beobtained.

The above document (4) discloses a method for maintaining mutualinductance that varies according to the distance between transmittingand receiving coils by utilizing two series-connected loop coils throughwhich currents flow in opposite directions. This may be utilized onlywhen the central axes of transmitting/receiving coils are aligned witheach other, but it is difficult to freely position a receiver on aplate-shaped transmitter, and it is also difficult to charge multiplereceivers placed on the transmitter in a wireless manner.

DISCLOSURE Technical Problem

The present invention has been made keeping in mind the above problems,and an object of the present invention is to provide a near-fieldwireless power transfer system, which utilizes a structure having auniform Figure of Merit (FoM), that is, uniform mutual inductance,between a wireless power transmitter and a wireless power receiver, thusobtaining uniform efficiency regardless of the charging position of thereceiver using only a simple impedance matching circuit withoutseparately using a complicated adaptive impedance matching circuit orcontrol circuit as in the case of a conventional scheme, and thussimultaneously transmitting power without undergoing difficulty inimpedance matching even for wireless power transmission to multipleelectronic devices.

Technical Solution

First, when the characteristics of the present invention are summarized,a coil structure for wireless power transmission in accordance with anaspect of the present invention includes a coil part through whichcurrent flows in a direction of input current applied from a first endof the coil structure, the coil part being disposed between the firstend and a second end of the coil structure; and a coil part connected tothe coil part through which current flows in the direction of the inputcurrent, the coil part being concentrically formed with the coil partand configured such that current flows in a direction opposite to thatof the input current, wherein the coil structure transfers wirelesspower depending on mutual inductance with respective target coils,relative center positions of which are horizontally different from eachother.

The target coil may include either a single coil, a relative centerposition of which is horizontally movable, or multiple coils, relativecenter positions of which are located at horizontally differentpositions.

For each target coil, the coil structure may be configured to haveuniform mutual inductance within a preset range.

The coil structure may be configured such that a magnetic field in acenter portion of the coil structure is relatively increased to haveuniformity in mutual inductance with another coil.

Coils constituting the coil structure may be formed using a PrintedCircuit Board (PCB) manufacturing process or a semiconductormanufacturing process, and coils formed to be distributed and arrangedon multiple layers are connected to each other through via holes.

Respective coil parts of the coil structure may be wound in shapes ofconcentric circles or concentric polygons.

The coil part through current flows in the direction of the inputcurrent may include a coil part concentrically wound multiple timestowards a center thereof so that current flows in the direction of theinput current.

The coil part through which the current flows in the direction oppositeto that of the input current may include a coil part in which two ormore coils are connected in parallel and wound so that current flows ina direction opposite to that of the input current.

The coil part in which two or more coils are connected in parallel andwound may be wound one or more times.

Further, in accordance with another aspect of the present invention,there is provided a coil structure includes a coil part through whichcurrent flows in a direction of input current applied from a first endof the coil structure, the coil part being disposed between the firstend and a second end of the coil structure, wherein the coil partincludes a first coil part concentrically wound one or more timestowards a center thereof so that current flows in a direction of theinput current; and a second coil part, a center of which is aligned withthat of the first coil part and in which two or more coils are connectedin parallel and are concentrically wound so that current flows in thedirection of the input current, and wherein the coil structure transferswireless power depending on mutual inductance with respective targetcoils, relative center positions of which are horizontally differentfrom each other.

The second coil part in which two or more coils are connected inparallel and are concentrically wound may be wound one or more times.

The coil structure may further include a third coil part in which two ormore coils are connected in parallel and are concentrically wound sothat current flows in a direction opposite to that of the input current.

The second coil part may be arranged in a center portion or an outermostportion of the coil structure.

In according to a further aspect of the present invention, there isprovided a wireless power transfer system for transmitting/receivingpower between a transmitting coil of a transmitter and a receiving coilof a receiver via magnetic coupling, wherein the transmitting coil orthe receiving coil includes a first coil part concentrically wound oneor more times towards a center thereof so that current flows in adirection of input current applied from a first end of the transmittingor receiving coil, the first coil part being disposed between the firstend and a second end of the transmitting or receiving coil; and a coilpart connected to the first coil part in which the current flows in thedirection of the input current, the coil part having a center alignedwith that of the first coil part and being concentrically arranged withthe first coil part, the coil part being configured such that currentflows in a direction opposite to that of the input current; or a coilpart having a center aligned with that of the first coil part, the coilpart being configured such that two or more coils are connected inparallel and are concentrically wound so that current flows in adirection of the input current, wherein the transmitting coil transmitspower to one or more receiving coils, relative center positions of whichare horizontally different from each other.

Uniform mutual inductance within a preset range may be obtained betweeneach of the receiving coils and the transmitting coil.

The transmitter or the receiver may transfer power using the uniformmutual inductance, without changing impedance matching.

The transmitter may include means for impedance matching to thetransmitting coil between an Alternating Current (AC) source (Vs) andthe transmitting coil.

The transmitter may include a source coil connected to the AC sourcethat is a voltage source, current source, power source, etc. and coupledto the transmitting coil via a time-varying magnetic field without beingdirectly connected electrically to the transmitting coil, and performimpedance matching via mutual inductance between the source coil and thetransmitting coil.

The wireless power transfer system may further include a capacitorarranged between a first end of the AC source and a first end of thesource coil. The capacitance of the capacitor may be variable dependingon the impedance variation and/or the number of the loads.

The transmitter may include a transformer for impedance matching, aprimary side of which is connected to an AC source that is a voltagesource, current source or power source, and a secondary side of which isconnected to the transmitting coil.

The transmitter may include a capacitor for impedance matching connectedbetween the transmitting coil and an AC source that is a voltage source,current source, or a power source.

The transmitter may include an inductor for impedance matching connectedbetween the transmitting coil and an AC source that is a voltage source,current source, or power source. The inductance of the inductor may bevariable depending on the impedance variation and/or the number of theloads.

The receiver may include means for impedance matching for a load, themeans being arranged between the receiving coil and the load.

The receiver may include a load coil connected to a load and coupled tothe receiving coil via a time-varying magnetic field without beingdirectly connected to the receiving coil, and perform impedance matchingvia mutual inductance between the receiving coil and the load coil.

The receiver may further include a capacitor arranged between a firstend of the load coil and a first end of the load.

The receiver may include a transformer for impedance matching, a primaryside of which is connected to the receiving coil and a secondary side ofwhich is connected to a load.

The receiver may further include a capacitor arranged between a firstend of the secondary side and a first end of the load.

The receiver may include an inductor for impedance matching connectedbetween a load and the receiving coil.

The receiver may include a capacitor for impedance matching connectedbetween a load and the receiving coil.

The wireless power transfer system may further include a capacitorarranged between a first end of the inductor and a first end of theload.

The transmitter may include a sensing circuit for sensing a variation inloads (for example, the magnitude or the phase of the voltage or thecurrent) depending on a number of receiving coils, and perform impedancematching by controlling the means for impedance matching so that inputimpedance is adjusted depending on the variation in the loads sensed bythe sensing circuit.

In accordance with yet another aspect of the present invention, there isprovided a wireless power transmission method, including transmitting,by a transmitting coil, power in a wireless manner by using an ACsource; and receiving, by a receiving coil via magnetic coupling, thepower in a wireless manner, wherein the transmitting coil or thereceiving coil includes a first coil part concentrically wound one ormore times towards a center thereof so that current flows in a directionof input current applied from a first end of the transmitting orreceiving coil, the first coil part being disposed between the first endand a second end of the transmitting or receiving coil; and a coil partconnected to the first coil part in which the current flows in thedirection of the input current, the coil part having a center alignedwith that of the first coil part and being concentrically arranged withthe first coil part, the coil part being configured such that currentflows in a direction opposite to that of the input current; or a coilpart having a center aligned with that of the first coil part, the coilpart being configured such that two or more coils are connected inparallel and are concentrically wound so that current flows in adirection of the input current, wherein transmitting the power in thewireless manner is configured such that the transmitting coil transmitspower to one or more receiving coils, relative center positions of whichare horizontally different from each other.

Advantageous Effects

In accordance with the near-field wireless power transfer systemaccording to the present invention, there is no need to use a circuitfor changing impedance matching depending on a change in the positionbetween a transmitter and a receiver, and thus system complexity isdecreased, and the system costs are low.

Further, the present invention enables free positioning by which atransmitter and a receiver are freely arranged using a single coilwithin the range of a wireless power transmission distance or aneffective wireless charging range, which has a uniform mutual inductanceof 20% or less, without requiring a separate additional circuit.

Furthermore, since uniform mutual inductance is obtained within awireless power transmission distance having uniform mutual inductance,multiple devices may simultaneously receive wireless power and mayprovide power for operations of the respective devices or may be chargedwith power.

DESCRIPTION OF DRAWINGS

FIG. 1 is an equivalent circuit diagram of a typical electromagneticinduction-type wireless power transfer system that uses respectiveresonant coils of a transmitter and a receiver;

FIG. 2 is a diagram showing the concept of a wireless power transfersystem according to an embodiment of the present invention;

FIG. 3 is a graph showing maximum transmission/reception power transferefficiency depending on the FOM of the wireless power transfer systemaccording to an embodiment of the present invention;

FIGS. 4A and 4B are diagrams showing an example of calculation resultsof mutual inductance M₁₂ between the transmitting and receiving coils inthe wireless power transfer system according to an embodiment of thepresent invention;

FIG. 5 is a diagram showing an example of a coil structure havingelectrically uniform mutual inductance according to an embodiment of thepresent invention;

FIG. 6 is a diagram illustrating a coil actually manufactured to havethe structure of FIG. 5;

FIG. 7 is a diagram illustrating an actually manufactured receiving coilaccording to an embodiment of the present invention;

FIG. 8 is a diagram showing the results of measuring mutual inductancebetween the transmitting and receiving coils of the wireless powertransfer system according to an embodiment of the present invention;

FIG. 9 is a diagram showing a configuration in which the proposed coilstructure of FIG. 5 is applied to the transmitter of the wireless powertransfer system according to an embodiment of the present invention;

FIG. 10 is a diagram showing a detailed configuration in which theproposed coil structure of FIG. 5 is applied to the transmitter of thewireless power transfer system according to an embodiment of the presentinvention;

FIG. 11 is a diagram showing another detailed configuration in which theproposed coil structure of FIG. 5 is applied to the transmitter of thewireless power transfer system according to an embodiment of the presentinvention;

FIG. 12 is a diagram showing a further detailed configuration in whichthe proposed coil structure of FIG. 5 is applied to the transmitter ofthe wireless power transfer system according to an embodiment of thepresent invention;

FIG. 13 is a diagram showing yet another detailed configuration in whichthe proposed coil structure of FIG. 5 is applied to the transmitter ofthe wireless power transfer system according to an embodiment of thepresent invention;

FIG. 14 is a diagram showing the configuration of the receiver of thewireless power transfer system according to an embodiment of the presentinvention;

FIG. 15 is a diagram showing the detailed configuration of the receiverof the wireless power transfer system according to an embodiment of thepresent invention;

FIG. 16 is a diagram showing another detailed configuration of thereceiver of the wireless power transfer system according to anembodiment of the present invention;

FIG. 17 is a diagram showing a further detailed configuration of thereceiver of the wireless power transfer system according to anembodiment of the present invention;

FIG. 18 is a diagram showing yet another detailed configuration of thereceiver of the wireless power transfer system according to anembodiment of the present invention;

FIG. 19 is a diagram showing still another detailed configuration of thereceiver of the wireless power transfer system according to anembodiment of the present invention;

FIG. 20 is a diagram illustrating a case where the structures of FIGS.11 and 15 are coupled to each other; and

FIG. 21 is a diagram showing variations in magnetic fields in theproposed coil structure of FIG. 5, a structure in which N₃ and N₄ areremoved from the structure of FIG. 5, and a structure in which only N₄is removed from the structure of FIG. 5.

BEST MODE

Preferred embodiments of the present invention will be described indetail with reference to the attached drawings and details described inthe drawings. However, the present invention is not limited orrestricted by the above embodiments.

FIG. 2 is a diagram showing the concept of a wireless power transfersystem according to an embodiment of the present invention.

As shown in FIG. 2, the wireless power transfer system according to theembodiment of the present invention includes matching units (Tx matchingunit and Rx matching unit) for impedance matching respectively providedin a transmitter for receiving an AC source (Vs) and a receiver so thatthe transmitting (resonant) coil (Tx coil, indicated by self-inductanceL₁, resistance R₁, and capacitance C₁ for resonance in an equivalentcircuit) of the transmitter may transmit the maximum power to thereceiving (resonant) coil (Rx coil, indicated by self-inductance L₂,resistance R₂ and capacitance C₂ for resonance in an equivalent circuit)of the receiver via electromagnetic induction or magnetic coupling basedon mutual inductance M₁₂.

In order to transfer the maximum power, the impedance matching unit ofthe transmitter (Tx matching unit) must minimize the reflection of asource signal that is transmitted by matching impedance viewed from theTx coil to input impedance Z_(in) (impedance viewed from a source), andthe impedance matching unit of the receiver (Rx matching unit) forobtaining the effect of impedance matching for a load (impedance Z_(L))must satisfy the condition of conjugate matching of impedance viewedfrom the Rx coil towards the load.

In this case, when conductance resistance loss caused by the matchingunit (Tx matching unit or Rx matching unit) is not present, a maximumpower transfer efficiency η (the ratio of power transferred to a load tototal transmitted power) may be derived based on well-knownelectromagnetic theory by the following Equation 1:

$\begin{matrix}{{\eta = \frac{( {1 + {FOM}^{\; 2}} )^{\frac{1}{2}} - 1}{( {1 + {FOM}^{\; 2}} )^{\frac{1}{2}} + 1}}{{FOM} = \frac{( {2\pi \; f_{r}} )M_{12}}{( {R_{1}R_{2}} )^{\frac{1}{2}}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where FOM denotes the Figure of Merit (FoM) of thetransmitting/receiving system. When a coil, which will be describedlater and which is proposed in the present invention, is used, if R₁ inEquation 1 is replaced with R_(p), the FOM and the maximum powertransfer efficiency η may be obtained. Here, f_(r) denotes the resonantfrequency of the Tx coil and the Rx coil, R₁ denotes the resistance ofthe Tx coil, R₂ denotes the resistance of the Rx coil, and M₁₂ denotesmutual inductance between the Tx and Rx coils. In Equation 1, theresistances of the Tx and Rx coils are scarcely changed due to changesin the positions of the Tx and Rx coils, and thus the efficiency η andthe FoM of the system vary according to M₁₂.

In the present invention, the transmitter may supply wireless power tothe above-described receiver mounted in various types of electronicdevices that consume power, such as a smart phone and a tablet such asiPad, at the maximum power transfer efficiency. The transmitter maysimply or inexpensively supply wireless power at the maximum powertransfer efficiency adaptively to free positioning, as will be describedlater, within the wireless power transmission range having an FoM of 20%or less or having a uniform mutual inductance M₁₂ based on theabove-described principle, even if a complicated adaptive impedancematching circuit for supporting the optimal impedance matching is notused depending on changes in the positions of the correspondingtransmitter and receiver in which the proposed coil structure of thepresent invention may be applied to one or more of the Tx coil and theRx coil when a wireless power transmitter transmits power to a receiverhaving a spatially fixed or movable load (e.g., a battery, a deviceoperating circuit, etc.). Since the present invention has uniform mutualinductance within a wireless power transmission distance having suchuniform mutual inductance, multiple devices may simultaneously receivewireless power, and use the power to charge a battery or operate thedevices.

FIG. 3 is a graph showing the transmission/reception maximum powertransfer efficiency η depending on the FoM of the wireless powertransfer system according to an embodiment of the present invention.Here, the maximum power transfer efficiency η indicates a case where theTx and Rx matching units satisfy the above-described maximum powertransfer condition. It can be seen that, as shown in FIG. 3, as the FoMincreases, efficiency 1 increases, whereas as the FoM decreases, avariation in the maximum power transfer efficiency η becomes larger witha variation in the FoM.

FIGS. 4A and 4B are diagrams showing an example of calculation resultsof mutual inductance M₁₂ between transmitting (Tx) and receiving (Rx)coils in the wireless power transfer system according to an embodimentof the present invention.

FIG. 4A, the Tx coil and the Rx coil are arranged in parallel with eachother so that the centers thereof are aligned with each other. Each ofthe coils having a radius of 10 cm is assumed to be a very thinfilamentary coil and to have a number of turns corresponding to 1. Allof units of numerals described in the drawing are cm. FIG. 4Billustrates a mutual inductance value appearing when the center of theRx coil is horizontally moving in a y direction by a movement distancerho in the drawing. Such transmission/reception configuration maygenerally be an example of a structure in which, when a receiver isplaced on a transmitter (e.g., a distance of 5 cm when the centers ofthe two coils are aligned with each other in the drawing), the receiveris charged in a wireless manner. As shown in the drawing, when thecenters of two coils are aligned with each other (y=0), a largest mutualinductance value is exhibited. As rho becomes larger, the mutualinductance value is gradually decreased and then becomes 0 near aposition where the difference between the centers is about 17 cm. Thatis, depending on a change in the relative horizontal positions of thetwo coils (one coil is moved horizontally along the plane of the coil),the distance between the centers of the two coils changes, and an areain which magnetic fields are coupled changes, thus varying the mutualinductance. For this reason, when the receiver is moving in the actualcharging zone of the transmitter, mutual inductance between the Tx andRx coils varies, so that an optimal power transfer condition changes.Accordingly, Tx/Rx matching units must be designed to satisfy themaximum power transfer condition in order to obtain the maximum powertransfer efficiency η according to the position.

FIG. 5 is a diagram showing an example of a coil structure according toan embodiment of the present invention to have electrically uniformmutual inductance. Referring to FIG. 5, a coil structure to have uniformmutual inductance according to an embodiment of the present invention iscomposed of concentrically arranged four parts N₁, N₂, N₃, and N₄ havingdifferent radiuses r₁, r₂, r₃, and r₄ from the identical center.

The outermost coil part N₁ is implemented as loop coil (s) that startsat one end of the coil structure for receiving an input current I₀ andthat is wound one or more times (e.g., three times) at equal intervals(p₁) (e.g., see 1.5 mm in the following Table 1) from an outermostradius r₁ (e.g., 6.5 cm in the following Table 1), wherein each loopcoil of N₁ has the same current (forward) direction as that of the inputcurrent. Here, although the loop coils wound as the coil part N₁ havebeen described as being at equal intervals by way of example, they arenot limited to such an example and may be wound at unequal intervals.The remaining coils N₂, N₃, and N₄ may be respectively implemented ascoils wound multiple times, wherein the coils may have the shape ofbeing wound at equal or unequal intervals.

The coil part N₂ connected to and extended from the end of the coil partN₁ may preferably be a single coil wound to have a radius r₂ (e.g., see6 cm in the following Table 1) smaller than that of the innermost coilof the coil part N₁ (according to the circumstances, N₂ may havemultiple coils). The loop coil(s) of the coil part N₂ is spaced apartfrom the innermost coil among the coils of the coil part N₁ by apredetermined interval, which is preferably different from the intervalp_(i) between the coils of the coil part N₁ (according to thecircumstances, the interval may be identical to the interval p₁).

The coil part N₃ connected to the end of the coil part N₂ is a coilwound to have an outermost radius r₃ (e.g., see 5.5 cm in the followingTable 1) smaller than the radius r₂ inside a circle defined by theradius r₂, and is configured such that two coils are connected inparallel with each other at a predetermined interval (e.g., see 5 mm inthe following Table 1) (according to the circumstances, three or morecoils may be connected in parallel, and the intervals between the coilsmay be unequal), wherein the coils of the coil part N₃ are formed to bewound one or more times so that the current direction of N₃ is opposite(reverse) to that of the coil parts N₁ and N₂.

The coil part N₄ connected to the end of the coil part N₃ (the end ofthe two connected coils) is a coil wound to have a radius r₄ (e.g., see4.5 cm in the following Table 1) smaller than the radius of the innercoil of the coil part N₃, and may have a shape in which two coils areconnected in parallel with each other at a predetermined interval (e.g.,15 mm in the following Table 1) (according to the circumstances, threeor more coils may be connected in parallel and the intervals between thecoils are unequal), wherein the coil part N₄ is formed to be wound oneor more times so that the current direction of the coil part N₄ isidentical to that of the coils of the coil parts N₁ and N₂. A capacitorCp may be connected, for adjustment of a resonant frequency or forimpedance matching, to a suitable position corresponding to any one ofbetween the end portion of the coil part N₄ (the end of two connectedcoils) and the start portion of the coil part N₁, the end portion of thecoil part N₄, and the start portion of the coil part N₁, as shown inFIG. 6.

In FIG. 5, input current I₀ applied to the coil part N₁ is divided intoαI₀ and (1−α)I₀ at the parallel coils of the coil part N₃ and flowsthrough the coils. Similarly, the input current is divided into βI₀ and(1−β)I₀ at the parallel coils of the coil part N₄ and flows through thecoils. α and β may be either positive or negative numbers, and themagnitudes of the absolute values thereof are equal to or less than 2.Therefore, in case for N3, the cases of (α=−1, 1−α=2), (α=1, 1−α=0),(α=0, 1−α=1), etc. are possible. These cases may occur because N3 isinfluenced by the magnetic field resulting from the current flowing inthe neighboring coil. In case for N4, the cases of (β=−1, 1−β=2), (β=1,1−β=0), (β=0, 1−β=1), etc. are possible.

In this way, although, in the proposed coil structure of the presentinvention, an example in which the respective coil parts are formed inthe shape of concentric circles has been described, the coil structureis not limited to such an example and may be formed in the shape ofvarious concentric polygons, such as a rectangular shape or a hexagonalshape, if necessary. Further, an example in which each coil part isformed using a metal conducting wire such as a copper wire has beendescribed, as shown in FIG. 6, but the pattern of each coil part may beformed using various manufacturing processes according to thecircumstances, such as a Printed Circuit Board (PCB) manufacturingprocess or a semiconductor manufacturing process. When such a PCBmanufacturing process or semiconductor manufacturing process is used,four coil parts N₁, N₂, N₃, and N₄ may be suitably distributed andarranged on multiple layers, such as both surfaces of a given board suchas a PCB or a semiconductor wafer, wherein the coil parts formed on therespective layers may be connected to each other through via holes orthe like.

Further, although the arrangement of the respective coils N₁, N₂, N₃,and N₄ has been illustratively shown, as shown in FIG. 5 or 6, thearrangement is not limited thereto, and the coils N₁, N₂, N₃, and N₄ maybe freely arranged without being limited to specific positions.Furthermore, some of the coil parts N₁, N₂, N₃, and N₄ may be omitted.In this case, individual coil parts may be suitably connected betweenone end and the other end of the coil structure, and the coil part N₄may also be arranged in the outermost portion of the coil structurerather than the center portion (innermost portion) thereof as in thecase of FIGS. 5 and 6.

TABLE 1 Number of Coil Direction & Turns Pitch Radius thicknessconnection N₁ 3 1.5 mm 6.5 cm 0.64 mm Forward & series N₂ 1 — 6 cm 0.64mm Forward & series N₃ 2 5 mm 5.5 cm 0.64 mm Reverse & parallel N₄ 2 15mm 4.5 cm 0.64 mm Reverse & parallel

FIG. 7 illustrates an actually manufactured receiving coil (Rx coil)according to an embodiment of the present invention. The Rx coil may bemanufactured using a PCB manufacturing process, and the resonantfrequency f_(r) thereof is set to 6.78 MHz. In addition, the Rx coil mayalso be manufactured using the above-described various methods, such asa method using a thin copper wire or a semiconductor manufacturingprocess. Such an Rx coil is a single exemplary structure, and the coilstructure of the present invention such as that shown in FIG. 5 or 6 mayalso be applied to the Rx coil. That is, both the transmitting coil (Txcoil) and the receiving coil (Rx coil) may be formed in the shape of thecoil structure of the present invention, such as that shown in FIG. 5 or6. Alternatively, only either the Tx coil or the Rx coil may be formedin the shape of the coil structure of the present invention, such asthat shown in FIG. 5 or 6.

FIG. 8 illustrates the measurement results of mutual inductance M₁₂between the transmitting and receiving coils of the wireless powertransfer system according to an embodiment of the present invention.

A capacitor Cp may be connected to a suitable position corresponding toany one of between the end portion of the coil part N₄ (the end of twoconnected coils) and the start portion of the coil part N₁, the endportion of the coil part N₄, and the start portion of the coil part N₁,as shown in FIG. 6, so that both the Tx coil and the Rx coil have aresonant frequency of 6.78 MHz.

In FIG. 8, graph a and b indicate mutual inductance between a Tx coilhaving a conventional coil structure in which only coil parts N₁ and N₂other than the coil parts N₃ and N₄ in the structure of FIG. 6 are used,and an Rx coil having the structure such as that shown in FIG. 7, andshow mutual inductances for case 1 (where the center of the Rx coil ismoved from the position of the coordinates of FIG. 4A in a y direction)and case 2 (where the center of the Rx coil is moved from the positionof the coordinates of FIG. 4A in an X direction). In FIG. 8, graphs cand d indicate mutual inductance between the Tx coil having thestructure of FIG. 6 and the Rx coil having the structure of FIG. 7, andshow mutual inductances for case 1 (where the center of the Rx coil ismoved from the position of the coordinates of FIG. 4A in a y directionthat is horizontal to a coil surface) and case 2 (where the center ofthe Rx coil is moved from the position of the coordinates of FIG. 4A inan x direction that is horizontal to the coil surface).

As shown in FIG. 8, when a distance ρ (rho) between the centers of twocoils is changed in a charging zone that is a portion processed as acolored portion in graph a, a variation in mutual inductance is verylarge (e.g., (maximum mutual inductance−minimum mutualinductance)/maximum mutual inductance>0.2). However, in a charging zonein which a difference between the centers of the two coils is 4 cm orless, a variation in mutual inductance is very small (e.g., (maximummutual inductance−minimum mutual inductance)/maximum mutualinductance<0.2) in graph c. It can be seen that when the distancedeviates from the charging zone, mutual inductance rapidly decreases forall cases.

MODE FOR INVENTION

FIG. 9 is a diagram showing a configuration in which the proposed coilstructure such as that shown in FIG. 5 is applied to the transmitter ofthe wireless power transfer system according to an embodiment of thepresent invention.

As shown in FIG. 5, both ends of a coil proposed in the presentinvention and composed of four parts N₁, N₂, N₃, and N₄ having differentradiuses r₁, r₂, r₃, and r₄ to have uniform mutual inductance accordingto an embodiment of the present invention may be connected to both endsof the impedance matching unit (Tx matching unit) of the transmitter,and thus the proposed coil may be used as a Tx coil. In this case, theentirety of the proposed coil that is the Tx coil may be equivalentlyimplemented using resistance R_(p) and inductance L_(p), and a capacitorC_(p) may be connected between one end of the proposed coil that is theTx coil and one end of the impedance matching unit of the transmitter(Tx matching unit). C_(p) is used to adjust a resonant frequency andperform impedance matching. In addition, the capacitor Cp may beconnected in various connection shapes, such as connection between theend portion of the coil part N₄ and the start portion of the coil partN₁.

FIG. 10 is a diagram showing a detailed configuration in which theproposed coil structure such as that shown in FIG. 5 is applied to thetransmitter of the wireless power transfer system according to anembodiment of the present invention.

As shown in FIG. 10, the transmitter is configured such that a sourcecoil (indicated by self-inductance L_(s) and resistance R_(s) in anequivalent circuit) is connected between both ends of an AC source Vs(voltage source, current source, or power source), and a capacitor C_(s)may be connected to one end of the source coil, and such that a proposedcoil (indicated by self-inductance L_(p) and resistance R_(p) in anequivalent circuit) having a capacitor C_(p), which is a transmitting(resonant) coil (Tx coil) coupled magnetically to the source coil, isprovided.

The source coil and the transmitting (resonant) coil (Tx coil) are notdirectly connected and are coupled to each other via a magnetic fieldwhile being spaced apart from each other, and function as an impedancematching unit (Tx matching unit) by performing impedance matching viathe adjustment of mutual inductance M₁ between the source coil and thetransmitting (resonant) coil (Tx coil). Further, a capacitor C_(s)between one end of the AC source Vs and one end of the source coil maybe used for the resonance of the source coil with the Tx (resonant) coil(Tx coil), but it is not necessarily required.

FIG. 11 is a diagram showing another detailed configuration in which theproposed coil structure such as that shown in FIG. 5 is applied to thetransmitter of the wireless power transfer system according to anembodiment of the present invention.

As shown in FIG. 11, the transmitter is configured such that the primaryside of a transformer (indicated by inductance L_(S1) and resistanceR_(S1) in an equivalent circuit) is connected between both ends of an ACsource Vs (voltage source, current source, or power source), and suchthat a Tx (resonant) coil (Tx coil) that is a proposed coil (indicatedby self-inductance L_(p) and resistance R_(p) in an equivalent circuit)having a capacitor C_(p) connected between both ends of the proposedcoil is provided on the secondary side of the transformer (indicated byself-inductance L_(T1) and resistance R_(T1) in an equivalent circuit).Here, the transformer functioning as an impedance matching unit (Txmatching unit) may have a structure in which primary side and secondaryside coils are wound around an air core, or may have a structure inwhich primary side and secondary side coils are wound around a materialcontaining a magnetic material, such as a ferrite core.

FIG. 12 is a diagram showing a further detailed configuration in whichthe proposed coil structure such as that shown in FIG. 5 is applied tothe transmitter of the wireless power transfer system according to anembodiment of the present invention.

As shown in FIG. 12, the transmitter is configured such that a capacitorC_(m1) functioning as an impedance matching unit (Tx matching unit) isconnected between both ends of an AC source Vs (voltage source, currentsource, or power source) and such that a proposed coil (indicated byself-inductance L_(p) and resistance R_(p) in an equivalent circuit)having a capacitor C_(p) may be provided in parallel with the capacitorC_(m1) as a Tx (resonant) coil (Tx coil).

FIG. 13 is a diagram showing yet another configuration in which theproposed coil structure such as that shown in FIG. 5 is applied to thetransmitter of the wireless power transfer system according to anembodiment of the present invention.

As shown in FIG. 13, the transmitter is configured such that an inductorL_(m1) functioning as an impedance matching unit (Tx matching unit) isconnected between both ends of an AC source Vs (voltage source, currentsource, or power source), and such that a proposed coil (indicated byself-inductance L_(p) and resistance R_(p) in an equivalent circuit)having a capacitor C_(p) may be provided in parallel with the inductorL_(m1) as a Tx (resonant) coil (Tx coil).

In addition to the methods of FIGS. 10 to 13 for impedance matching,matching circuits that exploit various types of coupling elements, suchas a coil, a transformer, a capacitor, and an inductor, may be used.

FIG. 14 illustrates the configuration of the receiver of the wirelesspower transfer system according to an embodiment of the presentinvention. As described above, the coil structure such as that shown inFIG. 7 or the proposed coil structure such as that shown in FIG. 5 maybe applied to the receiving (resonant) coil (Rx coil), which will bedescribed later.

As shown in FIG. 14, the receiver includes an Rx (resonant) coil (Rxcoil) (indicated by self-inductance L₂, resistance R₂, and capacitanceC₂ in an equivalent circuit) of the receiver, coupled to a Tx (resonant)coil (Tx coil) via mutual inductance M₁₂, and a matching unit (Rxmatching unit) for impedance matching connected between both ends of theRx coil, and has a structure in which a load (impedance Z_(L)) isconnected between both ends of the Rx matching unit to consume power.The load (impedance Z_(L)) may be a circuit for the charging of abattery or the operation of a device. C₂ is used to adjust the resonantfrequency of the Rx coil and perform impedance matching of the Rx coil.

FIG. 15 is a diagram showing a detailed configuration of the receiver ofthe wireless power transfer system according to an embodiment of thepresent invention.

As shown in FIG. 15, the receiver includes an Rx (resonant) coil (Rxcoil) (indicated by self-inductance L₂, resistance R₂, and capacitanceC₂ in an equivalent circuit) that is an Rx self-resonant coil, and aload coil (indicated by self-inductance L_(L) and resistance R_(L) in anequivalent circuit) coupled to the Rx coil via magnetic coupling, andhas a structure in which a capacitor C_(L) may be connected to one endof the load coil and a load (impedance Z_(L)) is connected between bothends of the load coil (or between both ends of the load coil afterpassing through the capacitor C_(L)) to consume power. The capacitorC_(L) between one end of the load coil and one end of the load(impedance Z_(L)) may be used to adjust the resonant frequency of theload coil and the source coil or perform impedance matching of the loadcoil, but it is not necessarily required and may be omitted according tothe circumstances. Here, by performing impedance matching via theadjustment of mutual inductance M_(L) between the Rx (resonant) coil (Rxcoil) and the load coil, the Rx coil and the load coil may function asan impedance matching unit (Rx matching unit).

FIG. 16 illustrates another detailed configuration of the receiver ofthe wireless power transfer system according to an embodiment of thepresent invention.

As shown in FIG. 16, the receiver is configured such that a primary sideof a transformer (indicated by self-inductance L_(T2) and resistanceR_(T2) in an equivalent circuit) is connected between both ends of an Rx(resonant) coil (Rx coil) (indicated by self-inductance L₂, resistanceR₂, and capacitance C₂ in an equivalent circuit) that is a Rxself-resonant coil, and such that a load (impedance Z_(L)) is connectedbetween both ends of a secondary side of the transformer (indicated byself-inductance L_(L2) and resistance R_(L2) in an equivalent circuit)(or between both ends of the secondary side after passing through acapacitor C_(L2)) to consume power. The capacitor C_(L2) between one endof the secondary side of the transformer and one end of the load(impedance Z_(L)) may be used for impedance matching, but it is notnecessarily required and may be omitted according to the circumstances.Here, the transformer functioning as an impedance matching unit (Rxmatching unit) may have a structure in which primary and secondary sidecoils are wound around an air core or may have a structure in whichprimary side and secondary side coils are wound around a materialcontaining a magnetic material, such as a ferrite core.

FIG. 17 illustrates a further detailed configuration of the receiver ofthe wireless power transfer system according to an embodiment of thepresent invention.

As shown in FIG. 17, the receiver is configured such that an inductorL_(m2) functioning as an impedance matching unit (Rx matching unit) isconnected between both ends of an Rx (resonant) coil (Rx coil)(indicated by self-inductance L₂, resistance R₂, and capacitance C₂ inan equivalent circuit) that is an Rx self-resonant coil, and such that aload (impedance Z_(L)) is connected between both ends of the inductorL_(m2) (or both ends of the inductor L_(m2) after passing through acapacitor C_(m)) to consume power. The capacitor C_(m) between one endof the inductor L_(m2) and one end of the load (impedance Z_(L)) may beused for impedance matching, but it is not necessarily required and maybe omitted according to the circumstances.

FIG. 18 illustrates yet another detailed configuration of the receiverof the wireless power transfer system according to an embodiment of thepresent invention.

As shown in FIG. 18, the receiver is configured such that a capacitorC_(m) functioning as an impedance matching unit (Rx matching unit) isconnected between both ends of an Rx resonant coil (indicated byself-inductance L₂, resistance R₂, and capacitance C₂ in an equivalentcircuit) that is an Rx self-resonant coil, and such that a load(impedance Z_(L)) is connected between both ends of the capacitor C_(m)to consume power.

FIG. 19 is a diagram showing still another detailed configuration of thereceiver of the wireless power transfer system according to anembodiment of the present invention.

As shown in FIG. 19, the receiver is configured such that an inductorL_(m2) functioning as an impedance matching unit (Rx matching unit) isconnected between both ends of an Rx (resonant) coil (Rx coil)(indicatedby self-inductance L₂, resistance R₂, and capacitance C₂ in anequivalent circuit) that is an Rx self-resonant coil, and such that aload (impedance Z_(L)) is connected between both ends of the inductorL_(m2) to consume power. This illustrates a case where the capacitorC_(m) is omitted from the structure of FIG. 17.

FIG. 20 illustrates a case where the structures of FIGS. 11 and 15 arecoupled to each other.

As shown in FIG. 20, the transmitter is configured such that the primaryside of a transformer (indicated by inductance L_(S1) and resistanceR_(S1) in an equivalent circuit) is connected between both ends of an ACsource Vs (voltage source, current source, or power source), and suchthat a Tx (resonant) coil (Tx coil) that is a proposed coil (indicatedby self-inductance L_(p) and resistance R_(p) in an equivalent circuit)having a capacitor C_(p) connected between both ends of the proposedcoil is provided on the secondary side of the transformer (indicated byself-inductance L₁₁ and resistance R_(T1) in an equivalent circuit).Here, the transformer functioning as an impedance matching unit (Txmatching unit) may have a structure in which primary side and secondaryside coils are wound around an air core, or may have a structure inwhich primary side and secondary side coils are wound around a materialcontaining a magnetic material, such as a ferrite core.

Further, the receiver includes an Rx (resonant) coil (Rx coil) thereof(indicated by self-inductance L₂, resistance R₂, and capacitance C₂ inan equivalent circuit) coupled to the Tx (resonant) coil (Tx coil) viamutual inductance M₁₂, and a load coil (indicated by self-inductanceL_(L) and resistance R_(L) in an equivalent circuit) coupled to the Rxcoil via magnetic coupling, and has a structure in which a capacitorC_(L) may be connected to one end of the load coil and a load (impedanceZ_(L)) is connected between both ends of the load coil (or between bothends of the load coil after passing through the capacitor C_(L)) toconsume power. The capacitor C_(L) between the load coil and the load(impedance Z_(L)) may be used to adjust the resonant frequency of theload coil and the source coil or perform impedance matching of the loadcoil, but it is not necessarily required and may be omitted according tothe circumstances. Here, by performing impedance matching via theadjustment of mutual inductance M_(L) between the Rx (resonant) coil (Rxcoil) and the load coil, the Rx coil and the load coil may function asan impedance matching unit (Rx matching unit).

As described above, the near-field wireless power transfer systemaccording to the present invention enables free positioning in which thereceiver and the transmitter are freely arranged so that the centersthereof can be horizontally and relatively moved within a wireless powertransmission distance having a uniform mutual inductance of 20% or lessthrough the use of a single coil without requiring a separate additionalcircuit, as shown in FIG. 8. Further, the near-field wireless powertransfer system is configured such that multiple devices with relativecenter positions thereof located at horizontally different positionssimultaneously receive power in a wireless manner via their Rx coils,thus enabling power for the operations of respective devices or thecharging of the devices to be supplied. The present invention alsoapplies to the cases with a change in vertical position within apredetermined distance.

That is to say, when a mutual inductance is uniform between the Rx coiland the Tx coil which are spaced apart by a predetermined distance, themutual inductance is uniform within the charging area beyond thepredetermined distance.

In designing an optimal impedance matching circuit for maximum powertransmission reflecting on variations of the distance between the Rxcoil and the Tx coil, this eliminate the need of impedance matchingdepending on the positions of the Rx coil and the Tx coil within thecharging area, and only the impedance matching depending on thevariations of distance of the Rx coil and the Tx coil may suffice.

In this way, there is no need to use an adaptive impedance matchingcircuit depending on the change in the position between the transmitterand receiver, thus decreasing the complexity of the system and enablingthe system to be configured at low costs.

The coil structure having uniform mutual inductance may be present invarious shapes. In particular, the coil structure, such as that shown inFIG. 5 proposed in the present invention, uses a plurality ofseries-connected coils, and the respective coils N₁, N₂, N₃, and N₄ maybe connected at equal or unequal intervals. Further, there is astructure in which a plurality of coils are arranged in parallel witheach other, and such a parallel-connected structure may include coilsthrough which current flows in a direction opposite to that of inputcurrent, or coils through which current flows in a direction identicalto that of the input current. Although the arrangement of such coils N₁,N₂, N₃, and N₄ has been illustratively shown in FIGS. 5 and 6, thearrangement of the coils is not limited to such a specific arrangement,and the coils N₁, N₂, N₃, and N₄ may be arranged at any positions.

By means of the coil structure, a magnetic field in a weak magneticfield portion (center portion in the proposed coil structure) isincreased, and thus mutual inductance may be maintained so that apredetermined range around the coil structure (within a predetermineddistance from the center), for example, a condition of [(maximum mutualinductance-minimum mutual inductance)/maximum mutual inductance]<0.2, issatisfied on the whole. This is realized by adjusting the arrangement ofcoils, rather than changing the shapes of the coils. This was proved, asshown in FIG. 21, from the results of simulation. That is, FIG. 21illustrates the results of simulation of magnetic fields (H_(z)) atpositions higher than the respective coil structures H₁, H₂, and H₃ by aheight of 1 cm, wherein graph H₃ shows results obtained when N₃ and N₄are removed from the structure of FIG. 5, graph H₂ shows resultsobtained when N₄ is removed from the structure of FIG. 5, and graph H₁shows results obtained from the structure of FIG. 5 without change. Ascan be seen from FIG. 21, H₂ and H₃ indicate a large difference betweena magnetic field at the center (radial displacement, rho=0) and amagnetic field at a position where the center of the corresponding coilis horizontally moved in a y direction by 5 cm, but H₁ indicates that amagnetic field is very strong at the center, and decreases and thenincreases depending on the positions horizontally moving in the ydirection. As shown in FIG. 21, a magnetic field in a circumferentialportion in which a magnetic field is weaker than that of the center maybe reduced in the case of H₁ compared to H₂ or H₃. However, this is anexemplary result, and the magnetic field in the circumferential portionmay be increased or decreased depending on the arrangement status of thecoils N₁, N₂, N₃, and N₄, the number of turns of the coils, or the like.

By utilizing the coil structure having uniform mutual inductance,uniform mutual inductance or FoM is obtained even if the mutualpositions of the transmitter and the receiver are changed, and thus onlyan impedance matching circuit suitable for preset mutual inductanceneeds to be configured in the transmitter and the receiver. That is,there is no need to change suitable impedance matching depending on thepositions of the transmitter and the receiver. As shown in FIGS. 9 to20, the impedance matching circuit has various configurations.

Further, as in the case where respective receivers of multiple deviceswith relative center positions thereof located at horizontally differentpositions (permitting a change in vertical position within apredetermined distance) simultaneously receive power in a wirelessmanner via their Rx coils, when multiple loads are present, the inputimpedance Z_(in) of the transmitter may differ depending on the numberand positions of the Rx coils, but impedance matching may be easilyimplemented by applying the Tx coil having uniform mutual inductance asin the case of the present invention.

For example, since input impedance Z_(in) is changed depending on thenumber of receivers or Rx coils for such multiple loads, the system issimply implemented so that the transmitter performs impedance matchingby sensing a variation in loads depending on the change in the number ofreceivers or Rx coils via an input impedance (Z_(in)) sensing circuit(not shown) or voltage and/or current sensing circuit (not shown) and byadjusting the input impedance Z_(in) depending on only the number ofmultiple loads (receivers or Rx coils) regardless of the positions ofthe multiple loads.

Further, by inserting a separate Tx coil as shown in FIG. 10, the Txcoil is suitably designed to always have high efficiency even for themaximum number of loads and the number of loads below the maximumnumber, thus realizing impedance matching for multiple devices.

As in the case of the prior art, in a conventional non-uniform mutualinductance structure which does not have uniform mutual inductance,individual receivers have different mutual inductance values and have alarge variation in mutual inductance, and thus a problem arises in thatmultiple loads cannot be supported by a single transmitter. However, thepresent invention simply senses a variation in loads depending on thenumber of loads via an input impedance (Z₁) sensing circuit (not shown),and realizes impedance matching by controlling the resistance value,inductance value or capacitance value of the impedance matching unit (Txmatching unit) of the transmitter so that input impedance is adjusted inconformity with the sensed load variation, thus enabling wireless powerto be transmitted/received at maximum power transfer efficiency η. Thecontrol of the resistance value, inductance value or capacitance valueof the impedance matching unit (Tx matching unit) may be performed bycontrolling switching means (e.g., a Metal-Oxide Semiconductor FieldEffect Transistor (MOSFET), a Bipolar Junction Transistor (BJT), aSilicon Controlled Rectifier (SCR), a thyrister, or the like) so that aseparate resistor, inductor, or capacitor is added to or removed from acircuit.

As described above, although the present invention has been describedwith reference to limited embodiments and drawings, the presentinvention is not limited by the embodiments, and may be changed andmodified in various forms by those skilled in the art to which thepresent invention pertains from the description of the embodiments.Therefore, the scope of the present invention should not be limited anddefined by the above-described embodiments, and should be defined by theaccompanying claims and equivalents thereof.

1-37. (canceled)
 38. A wireless power transfer system for transmittingand receiving power between a transmitting coil of a transmitter and areceiving coil of a receiver via magnetic coupling, wherein: thetransmitting and receiving coils are configured such that centerpositions thereof are arranged at horizontally different positions toimplement wireless power transfer in a way of horizontally freepositioning, and are configured to transmit and receive power in awireless manner via uniform mutual inductance within a preset rangebetween the transmitting coil and the receiving coil.
 39. The wirelesspower transfer system of claim 38, wherein multiple devices placed athorizontally different positions simultaneously charge batteries thereofusing the uniform mutual inductance via receiving coils of correspondingreceivers.
 40. The wireless power transfer system of claim 38, whereinthe transmitter comprises: a unit for adjusting input impedance matchingof the transmitter depending on multiple loads placed at horizontallydifferent positions; and a sensing circuit for sensing a variation inthe input impedance looking into the transmitting coil depending on theloads and controlling the unit, thus performing impedance matching forthe multiple loads.
 41. The wireless power transfer system of claim 38,wherein: the transmitter comprises a unit for input impedance matchingof the transmitter between an Alternating Current (AC) source and thetransmitting coil, and the input impedance matching is possible via theunit within a range of a maximum number of multiple loads to be placedat horizontally different positions.
 42. The wireless power transfersystem of claim 41, wherein a source coil connected to the AC source isseparated from the transmitting coil via magnetic coupling, and theinput impedance matching is possible regardless of a variation in themaximum number of multiple loads by changing mutual inductance betweenthe source coil and the transmitting coil according to a design of thetransmitting coil.
 43. A coil structure, comprising: a coil part throughwhich current flows in a direction of input current applied from a firstend of the coil structure, the coil part being disposed between thefirst end and a second end of the coil structure; and a coil partconnected to the coil part through which current flows in the directionof the input current, the coil part being concentrically formed with thecoil part and configured such that current flows in a direction oppositeto that of the input current, wherein the coil structure transferswireless power depending on mutual inductance with respective targetcoils, relative center positions of which are horizontally differentfrom each other.
 44. The coil structure of claim 43, wherein the targetcoils comprise either a single coil, a relative center position of whichis horizontally movable, or multiple coils, relative center positions ofwhich are located at horizontally different positions.
 45. The coilstructure of claim 43, wherein the coil structure is configured suchthat a magnetic field in a center of the coil structure is relativelyincreased to have uniformity in mutual inductance with another coil. 46.The coil structure of claim 43, wherein coils constituting the coilstructure are formed using a Printed Circuit Board (PCB) manufacturingprocess or a semiconductor manufacturing process, and coils formed to bedistributed and arranged on multiple layers are connected to each otherthrough via holes.
 47. The coil structure of claim 43, whereinrespective coil parts of the coil structure are wound in shapes ofconcentric circles or concentric polygons.
 48. The coil structure ofclaim 43, wherein the coil part through current flows in the directionof the input current includes a coil part concentrically wound multipletimes towards a center thereof so that current flows in the direction ofthe input current.
 49. The coil structure of claim 43, wherein the coilpart through which the current flows in the direction opposite to thatof the input current comprises a coil part in which two or more coilsare connected in parallel and wound so that current flows in a directionopposite to that of the input current.
 50. The coil structure of claim49, wherein the coil part in which two or more coils are connected inparallel is wound one or more times.
 51. The coil structure of claim 49,wherein the coil part comprises two coils connected in parallel andinput current I₀ of the coil part is divided into αI₀ and (1−a)I₀through the two coils, wherein a is any number of which absolute valueis equal to or less than
 2. 52. A coil structure, comprising: a coilpart through which current flows in a direction of input current appliedfrom a first end of the coil structure, the coil part being disposedbetween the first end and a second end of the coil structure, whereinthe coil part comprises: a first coil part concentrically wound one ormore times towards a center thereof so that current flows in a directionof the input current; and a second coil part, a center of which isaligned with that of the first coil part and in which two or more coilsare connected in parallel and are concentrically wound so that currentflows in the direction of the input current, and wherein the coilstructure transfers wireless power via magnetic coupling with respectivetarget coils, relative center positions of which are horizontallydifferent from each other.
 53. The coil structure of claim 52, whereinthe second coil part in which two or more coils are connected inparallel and are concentrically wound is wound one or more times. 54.The coil structure of claim 53, wherein the second coil part comprisestwo coils connected in parallel and input current I₀ of the second coilpart is divided into αI₀ and (1−α)I₀ through the two coils, wherein a isany number of which absolute value is equal to or less than
 2. 55. Thecoil structure of claim 52, further comprising a third coil part inwhich two or more coils are connected in parallel and are concentricallywound so that current flows in a direction opposite to that of the inputcurrent.
 56. The coil structure of claim 54, wherein the third coil partcomprises two coils connected in parallel and input current I₀ of thethird coil part is divided into βI₀ and (1−β)I₀ through the two coils,wherein 0 is any number of which absolute value is equal to or less than2.
 57. A wireless power transfer system for transmitting/receiving powerbetween a transmitting coil of a transmitter and a receiving coil of areceiver via magnetic coupling, wherein the transmitting coil or thereceiving coil comprises: a first coil part concentrically wound one ormore times towards a center thereof so that current flows in a directionof input current applied from a first end of the transmitting orreceiving coil, the first coil part being disposed between the first endand a second end of the transmitting or receiving coil; and a coil partconnected to the first coil part in which the current flows in thedirection of the input current, the coil part having a center alignedwith that of the first coil part and being concentrically arranged withthe first coil part, the coil part being configured such that currentflows in a direction opposite to that of the input current; or a coilpart having a center aligned with that of the first coil part, the coilpart being configured such that two or more coils are connected inparallel and are concentrically wound so that current flows in adirection of the input current, wherein the transmitting coil transmitspower to one or more receiving coils, relative center positions of whichare horizontally different from each other.
 58. The wireless powertransfer system of claim 57, wherein uniform mutual inductance within apreset range is obtained between each of the receiving coils and thetransmitting coil.
 59. The wireless power transfer system of claim 58,wherein the power is transferred because of the uniform mutualinductance, without changing impedance matching regardless of variationsof the horizontal position of the transmitter or the receiver.
 60. Thewireless power transfer system of claim 57, wherein the transmittercomprises means for impedance matching to the transmitting coil betweenan Alternating Current (AC) source (Vs) and the transmitting coil. 61.The wireless power transfer system of claim 57, wherein the transmittercomprises a source coil connected to the AC source that is a voltagesource, current source or power source, and separated from andmagnetically coupled to the transmitting coil without being directlyconnected to the transmitting coil, and performs impedance matching viamutual inductance between the source coil and the transmitting coil. 62.The wireless power transfer system of claim 57, wherein the transmittercomprises a transformer for impedance matching, a primary side of whichis connected to an AC source that is a voltage source, current source orpower source, and a secondary side of which is connected to thetransmitting coil.
 63. The wireless power transfer system of claim 57,wherein the transmitter comprises a capacitor for impedance matchingconnected between the transmitting coil and an AC source that is avoltage source, current source, or a power source.
 64. The wirelesspower transfer system of claim 63, wherein the capacitor is connected inparallel or in series with the transmitting coil.
 65. The wireless powertransfer system of claim 64, wherein another capacitor is connected inseries with the AC source when the capacitor is connected in parallelwith the transmitting coil.
 66. The wireless power transfer system ofclaim 64, wherein another capacitor is connected in parallel with the ACsource when the capacitor is connected in series with the transmittingcoil.
 67. The wireless power transfer system of claim 57, wherein thetransmitter comprises an inductor for impedance matching connectedbetween the transmitting coil and an AC source that is a voltage source,current source, or power source.
 68. The wireless power transfer systemof claim 67, wherein the inductor is connected in parallel with thetransmitting coil.
 69. The wireless power transfer system of claim 68,wherein a capacitor is connected in series between the AC source and theinductor.
 70. The wireless power transfer system of claim 57, whereinthe receiver comprises means for impedance matching for a load, themeans being arranged between the receiving coil and the load.
 71. Thewireless power transfer system of claim 57, wherein the receivercomprises a load coil connected to a load and magnetically coupled tothe receiving coil without being directly connected to the receivingcoil, and performs impedance matching by adjusting mutual inductancebetween the receiving coil and the load coil.
 72. The wireless powertransfer system of claim 62, wherein the receiver further comprises acapacitor arranged between a first end of the load coil and a first endof the load.
 73. The wireless power transfer system of claim 57, whereinthe receiver comprises a transformer for impedance matching, a primaryside of which is connected to the receiving coil and a secondary side ofwhich is connected to a load.
 74. The wireless power transfer system ofclaim 57, wherein the receiver comprises an inductor or a capacitor forimpedance matching connected between a load and the receiving coil. 75.The wireless power transfer system of claim 74, further comprising acapacitor arranged between a first end of the inductor and a first endof the load.
 76. The wireless power transfer system of claim 60, whereinthe transmitter comprises a sensing circuit for sensing a variation inloads depending on a number of receiving coils, and performs impedancematching by controlling the means for impedance matching so that inputimpedance is adjusted depending on the variation in the loads sensed bythe sensing circuit.